1. Technical Field
The present invention relates to telephone systems and more particularly to a subscriber's extension telephone that includes a wireless link between the telephone instrument and an associated telephone line, allowing a subscriber to relocate the telephone instrument at will, yet still make and receive telephone calls in a conventional manner.
2. Background Art
Since the invention of the telephone, personal communication between individuals has grown so that the majority of all individuals in the United States and many other countries all have telephone service readily available. Rather than reach a saturation point when each family has been equipped with a single telephone, the growth trend has continued so that at present many individuals or families have not one, but several telephones for use in their residences.
The use of second and third telephones as extension units throughout a residence has become increasingly widespread. Previously, when only one telephone was installed in a home a central location for this instrument was chosen. However, no single location is perfect; and as a result frequently the housewife while performing daily chores is forced to come some distance, particularly in a large home, to the location of the telephone either to make or receive telephone calls. If the subscriber is in the yard, porch or basement, etc., the lack of proximity to a telephone instrument often results in extra steps and possibly missing a telephone call if the subscriber is unable to respond within a reasonably short period of time after the commencement of a ringing signal announcing the incoming call. In the trend toward so-called outdoor living today, the subscriber is frequently required to go from the garden or patio to the nearest telephone to answer it. In many cases this may be a substantial distance.
Several solutions to this problem have been proposed. Among these are the use of a number of extension telephones placed in convenient locations throughout the residence. The other is the use of a multiplicity of telephone line jacks, all connected to the telephone line, allowing the subscriber to move a plug equipped telephone instrument from one location to another to always be within easy access. Still another, is the use of long extension cords to connect the telephone instrument to its associated terminal thus allowing limited freedom in relocating the telephone. Obviously, all of these solutions lack flexibility since the location of the extension telephone or the extension jack while useful at times will still on many occasions be inadequate.
The most satisfactory solution to the extension telephone problem lies in the use of a telephone extension instrument that requires no wire connections between the instrument and the telephone line. An instrument such as this utilizing radio waves between terminal equipment connected to the telephone line and the instrument itself permits the subscriber to locate the telephone instrument any place within a specified range of telephone line terminal equipment located in the home or other location thus permitting the subscriber to both receive and make telephone calls at some distance from that terminal. Such a wireless extension telephone could be taken to the garden, patio, basement, upstairs, downstairs, etc., and placed in any room in the house as well as possibly carried with the subscriber while visiting a neighbor, so that incoming telephone calls would not be missed and so that they might be rapidly answered without considerable moving about on the part of the subscriber. The advantages of a wireless telephone instrument for subscribers is readily apparent, particularly in the home.
However, it should be pointed out that this same type of instrument would find considerable use in restaurants and other commercial establishments where a person to whom an incoming call is directed would have the telephone brought to him for answering without the necessity for intervening extension cords or other connections. Obviously, the number of possible uses for wireless extension telephones are limited only by the imagination of the users.
Early attempts to provide wireless extension telephones are disclosed in U.S. Pat. No. 2,129,332 to Mastini issued Sept. 6, 1938 and U.S. Pat. No. 2,894,121 to R. P. Phillips which issued on July 7, 1959. Both of these patents disclose simple wireless extension telephones employing vacuum tubes. In both instances, incoming telephone calls cause a transmitter associated with the telephone line to generate a carrier signal which is detected by a remote receiver. Likewise, calls initiated at a remote unit are effected by turning on a transmitter, with the carrier signal being detected by a receiver associated with the telephone line. The obvious disadvantage of size and large battery requirement etc. stem from the utilization of vacuum tubes, while reliance on detection of carrier wave signals for supervision, i.e.: "on" and "off" hook signal dialing, etc., is less than satisfactory because of the possible effect of RF interference caused from extraneous sources.
A substantially improved wireless extension telephone is disclosed in U.S. Pat. No. 3,193,623, issued on July 6, 1965 to R. V. Burns et al. The disclosed wireless extension telephone consisted of transistorized remote base and extension units with the obvious advantages of miniaturization as well as low battery drain. Additionally, full duplex operation is disclosed. "Off" and "on" hook supervision and dialing are accomplished by means of tone generation and detection rather than the use of RF carrier techniques taught in many of the prior art patents. In the Burns et al patent a tone of a first audio frequency superimposed on the RF carrier provides "off" and "on" hook control from the remote unit and a second audio tone generated at the remote unit provides dial pulse control. A number of other units employing different techniques such as sequential control, "touch calling" signalling, etc., have been taught in U.S. Pat. Nos. 3,721,771, 4,039,760 and 4,053,717. All of the above units, however, suffer from one or more defects in the area of reliability, size, battery consumption or security. Accordingly, it is the object of the present invention to provide a new and improved wireless extension telephone overcoming those shortcomings found in many previous wireless extension telephones.